There are lots of resistances against oxytetracyclin in europe (e.g. staphylococcus, streptococcus, pasteurella, proteus...), I'm pretty sure there isn't a really better situation in the US. It's a systemic broad band antibiotic you should only use in certain indications (and in my opinion...never without vet's advice).
Side effects may be problems with digestion, because antibiotics always restrain phyiological gut bacteria, too. If the chameleon already has a renal or liver disfunction, oytretracyclin may make it worse. And be very careful not to use it in younger chameleons, it arrests calcification.
Hope my info can help you.